Electric initiator



April 18, 1961 e. A. NODDIN ELECTRIC INITIATOR Filed Sept. 9, 1957 RN Ymm MQ ND E0 '0 MN A E QM o W ELECTRIC INITIATOR George Adelbert Noddin,Sewell, N.J., assignor to E. I. du Pont de Nemours and Company,Wilmington, Del., a corporation of Delaware Filed Sept. 9, 1957, Ser.No. 682,768

' Claims. (1. 102-28) The present invention relates to a novel electricinitiator. More particularly, the present invention relates to a novelelectrically actuated nonviolent initiator stable at high temperatures.

In many applications of explosives, a nonviolent initiator, i.e. aninitiator which is substantially noiseless in operation and produces noshattering or disruptive eifects, is highly desirable. For example, inthe novel blasting method and arrangement described in detail incopending application Serial No. 618,217, filed October 25, 1956 and nowabandoned by G. A. Noddin and assigned to the present assignee,explosive connecting cord, which isessentially noiseless in operationand comprises a core of from 0.1 to grains per foot of length of a highexplosive within a metal sheath, is used as the above-surfaceexplosionconducting means, i.e. trunk line, in blasting operations. theconventional Primacord trunk line in order to decrease the noiseproduced by the operation, because when Primacord is used the noise itproduces constitutes a nuisance which on occasion has provoked law suitsorinjunctions which impede the operation. The trunk line of explosiveconnecting cord, however, has been initiated by conventional electricinitiators which produce an annoying loud bang or snap, and theelimination or reduction of such noise is much desired.

In addition, in the novel seismic prospecting method described in detailin copending application Serial No.

618,509, filed October 26, 1956 and now abandoned by D. L. Coursen andN. G. Johnson and assigned to the present assignee, improved seismicrecords are obtained by use of a length of the explosive connecting cordto such an initiator would make its adoption very desirable in manyother applications of explosives.

Accordingly, an object of the present invention is to provide anonviolent electric. initiator. Another object of the present inventionis to provide an easily assembled electric initiator characterized bysubstantially noiseless operation and the absence of shattering elfects.A further object of the present inventionis to provide a nonviolentinitiator, suitable for use in numerous applica:

tions of explosives.

I have found that the foregoing objects may be achieved when I provideas an electric initiator a thinwalled metal tube in which is positionedaxially a rigid cylnder in the bore of which is confined a smallquantity of lead azide, said tube being sealed by an ignition assembly.A

In accordance with the present invention, an initiating charge,comprising 0.03 to 0.6 grain of lead azide disposed within the centralbore. of a heavy-walled rigid cylinder whose outer to inner diameterratio is 2 or more is inserted axially in an open'ended tube and anignition assembly is sealed within one end of the tube.

The cord is used instead of conduct the initiating impulse from'thesurface of the ventional electric initiator on the surface of the groundis used to actuate the cord, such an initiator produces interferingshock waves and is noisy in functioning. The

\ noise produced, aside from the effect on seismic recordinginstruments, is of little import when the exploration is being carriedout in remote regions. However, in populated or industrialized sites,such a disturbance becomes an important problem to the seismicsurveyors.

. Moreover, in the method of joining metallic elements by means of awrapping of high explosives, which method is described in detail in US.Patent 2,367,206, a conventional initiator has been used to actuate thehigh explosive. Consequently, the violence and metal fragments of suchinitiators has caused undesirable metal-working and deformation in thearea of the metallic elements adjacent the initiator.

Obviously, a need exists for a nonviolent initiator, substantiallynoiseless in operation and producing no shattering effects, in all ofthe afore-mentioned applications. Furthermore, the substantiallynoiseless action of V In order to describe more fully the presentinvention, reference is made to the accompanying drawings, in which: 1

Figures 1 to 3 are sectional elevations of the initiator I of thepresent invention, showing various modifications of the ignitionassembly.

Figure 4 is a sectional view of a fuse or cord assembly incorporatingthe initiator of the present invention, which assembly is suitable foruse, for example, in the previously mentioned seismic prospectingmethod.

In all figures, identical parts are indicated by the same symbols. 1 iIn Figure l, 1 is a thin-walled tube of metal, plastic, etc., 2 is 'aheavy-walled rigid cylinder, preferably of lead, having a central bore,3 is a mass of lead azide contained within the bore of cylinder 2, 4 isa high-resistance bridgewire, Sindicates the lead wires, 6 is aresilient sealing plug, for example of rubber, and 7 indicatescircumferential crimps which maintain the sealing plug 6 and thecylinder 2 in proper position within the tube.

In Figure 2, 4 is a bridgewire surrounded by a coherent mass, or head,8, of an ignition composition, and in Figure 3, 8' is a loose mass of anignition composition which is in contact with the bridgewire 4'.

In Figure 4, the initiator as shown in Figure 2 is combined with alength of explosive connecting cord, a portion of which is indicated by9. The cord is shown butted against cylinder 2 and held in place by acircumferential crimp 10.

In operation, the current is applied to the lead wires and'passesthrough the high-resistance bridgewire producing heat which actuates thelead azide contained'within the bore of the rigid cylinder. In this formof the ignition assembly, the so-called exploding" bridgewire assembly,which is shown in Figure 1, the passage of high current through thebridgewire volatilizes it and hot particles of metal are thrown againstand ignite the lead azide, which, in this case, acts as a combinedignition-initiation composition. Alternatively,. an ignitioncomposition, such as a boron-red lead mixture, may be positioned, in theform of a bead'or a loose ignition charge, around the bridgewire, asshown in Figures 2 and 3. The passage of low firing currents through thedisposed as is shown in Figure3. In all cases,,.the

Patented Apr. 18, 1961 tiator assembly is nonviolent in functioning,which is clearly indicated by the failure of the initiator shell torupture. The initiator. of the present invention may-be combinedreadily, as shown in Figure 4, with a length of detonatable explosivecord, for example detonating fuse, or Primacord, or the explosiveconnecting cord, to form a blasting initiator assembly or the like, thedetonation of the lead azide within the cylinder causing initiation ofthe adjacent explosive cord.

The followlngexamples serve 'to illustrate specific embodiments of theinitiator of the present invention. However, they will be understood tobe illustrative only an not as limiting the invention in any manner. I

Figure 1 A number of initiators having the bead ignition system showninFigure 2 were assembled, in which the weight of the lead azide withinthe cylinder and the length of the cylinder, which was made of lead,were varied as indicated in the following table. Lengths of theconnecting cord were crimped in the initiators so that the cord wasbutted against the end of the heavy-walled cylinder, as shown in Figure4. In the tests, the initator Iu testing this initiator, no connectingcord was used. The lead azide within the initiator detonated completelywithout rupture of the shell.

Example 2 A number of initiators having the exploding bridgewireignition-system were assembled. Inassembling these initiators, the leadazide-containing lead cylinder was inserted in a metal capsule having a0.005-inch-thick bottom, the end of the cylinder being flush against thebottom of the capsule. The capsule then was inserted in the open-endedtube, one end of which then was sealed by the ignition assembly. Alength of Primacord was inserted and crimped in the other end of theshell, the

end of the Primacord being butted againstthe bottom of the capsule. Thelead azide-containing cylinder was varied as shown in the followingtable, and the Primacord was initiated in all cases without rupture ofthe initiator shell.

TA L II Distribution of Length of 03 1- Total Wt. of PbN (grains/ inder(in) PbN in Cylft.) inder (grains) Exa ple 3 In another series ofexperiments, anumbjer of initiators wereassembled having a B-grainchargeof loose 62/35/3 btsmuth/ selenium/ potassium chlorate ignitioncomposiwere used, and in all cases the Primacord was initiated by theunit.

Distribution of Length of Cyl- Total Wt. of

PbNa rains} inder (in.) PhN in Cylt5 indcr (grains) Example 4 Anarc-fired initiator was assembled by inserting a A -inch-long leadcylinder into the center portion of a -inch-long aluminum tube, thecylinder containing 0.6 grain of lead azide. A 1.5-grain charge of looselead azide was placed on top of the cylinder, and then the ignitionassembly was sealed into the tube, the assembly comprising a pair oflead wires maintained in the sealing plug so that there was a 0.010-inchgap between the bared ends of the lead wires, which ends were surroundedby the charge of loose lead azide. Upon application of an electriccurrent, the loose lead azide charge ignited and initiated the leadazide in the cylinder.

As shown in the foregoing examples, a quantity as low as 0.03. grain oflead azide in the initiator of the present invention is suflicient toinitiate a high explosive. Heretofore, initiating charges comprisingabout 5 grains of a high explosive such as lead azide were used ininitiators to insure consistent initiation, this quantity of highexplosive causing the undesirable violence. The initiator of thisinvention is basedupon the discovery that a column of lead azide withina rigid cylinder can be ignited by conventionalignition means even at aloading as low asabout 2.5 grains per foot and then when thecolumn is atleast Ms inch in length, consistent initiation of detonating fuse orconnecting cord can be obtained. Thus, as little as 0.03 grain of leadazide will produce consistent initiation of detonating fuse andconnecting cord. However, quantities up to. 0.6 grain of lead azidecentrally disposed in a rigid cylinder can be used without loss of thenonshattering and substantially noiseless characteristics desired,provided the lead azide column does not exceed a loading of about 60grains per foot. .At higher column loadings, regardless of the length ofthe column, appreciable shattering effects and noise cannot be avoided.The length of the rigid cylinder. containing the lead azide is criticalonly in the mini mum requirement, i.e., at lengths less than inch,inadequate, priming action is obtained. However, no advantage resultsfrom using a cylinder of over /2 inch in length. I

In summation, the lead azide will preferably be present in a quantity offrom 0.03 to 0.6 grain at a loading of from 2.5 to 60 grains per footand centrally positioned in a rigid cylinder A3 to /2 inch in length.Inherent in the foregoing is the fact that the lead azide column is ofthe same length as the rigid cylinder. The lead azide contained withinthe cylinder may be admixed with anotherhigh explosive such as PETN ornitromannite.

Thecylinder is constructed of a rigid-materialwhich is nonreactive-withthe lead azide. Although. lead has beenexemplified andflis preferred,other metals and their alloys, such as aluminum and steel, can be used.In

quiredrigidity are suitable.

The cylinder is positioned axially in an open-ended thin-walled tube ofmetal, plastic, etc. in igniting proximity to the ignition assembly. Thedimensions of the tube are not critical, the outer diameter of thecylinder being adjusted in relation to the inner diameter of the tubeand being so selected that the cylinder can be inserted into the tubeand crimped in place without difficulty. When the initiator is to becombined with detonatable explosive cord, the diameter of the tube isselected accordingly. Tubes of about inch in length were exemplified,but shorter tubes which are of a length sufiicient to contain thecylinder and the ignition assembly and longer tubes, i.e. up to about 3inches in length, are equally suitable. Of course, the tube wall must beof a thickness such that the ignition composition does not shatter it.

To protect the lead azide within the cylinder from water, a thin metalwall may be provided adjacent the cylinder, for example, by providing acapsule of thin metal which surrounds the sides and bottom of thecylinder as illustrated in Example 2. The thin bottom, which can be of athickness in the order of 0.005 inch, does not interfere with thefunctioning of the initiator. As an alternative method of protecting thelead azide, a sealant can be applied to the end of the cylinder oppositethe ignition assembly without interference with the functioning of theinitiator.

A variety of electrical ignition assemblies can be sealed into the tube,for example by a resilient plug, such as a rubber plug, of conventionaldesign, through which the customary lead wires are introduced into theinitiator.

These ignition assemblies include a bridgewire and bead arrangement, abridgewire inserted in a mass of loose ignition composition, thepreviously described "exploding bridgewire unit, and an arc-firingsystem in which the bridgewire is eliminated. .The exploding bridgewire.unit is especially advantageous because such a unit can be actuated onlyby application of very high firing currents. 'The specific ignition orburning composition used intheignition assembly is not critical to theinitiator of the present invention, any ignition composition being'prise a fuel-oxidant mixture, such as boron-red lead (Pb o silicon-redlead, manganese-bismuth trioxide, lead sulfocyanate-potassiumchlorate-calcium silicide, bismuth-selenium-potassium chlorate,diazodinitrophenolpotassium chlorate, and thelike, or a single compound,such as lead styphnate, tetrazene, or a loose charge of lead azide. I

The lack of violence of the initiators is apparent. No noise aside froma slight popping sound, was produced by any of the initiators. Visualinspection of the initiators showed that no tube rupture occurred,indicating the absence of shattering eifects. This lack of violencepresents an important safety feature. For example, when suitable foruse. Such ignition compositions usually comsix of the initiatorsdescribed in Example 2 were bunched together, actuation of the centralinitiator occurred without sympathetic actuation of the other fiveinitiators.

The heat stability of the initiator of the present invention likewisewas shown by a series of tests. In these tests, one group of theinitiators prepared as described in Example 3 was subjected toheat-cycle storage under conditions more severe than those normallyencountered in storage of initiators relative humidity and 65 F. to F.)for one month, and another group was maintained at F. for six weeks. Allthe initiators so treated actuated lengths of the connecting cord. Thetests made to illustrate the initiating ability of the present initiatorshow that the initiator is capable of actuating both the explosiveconnecting cord, which contains about 0.1 to 10 grain of PETN or RDX perfoot, and conventional detonating fuse such as Primacord," even when thecord or fuse is not positioned immediately adjacent the lead azide.

It will be obvious to those skilled in the art that many modificationsin the design and use of the initiator of the present invention arepossible without departure from the scope of the presentinvention. Iintend, therefore, to be limited only by the following claims.

I claim:

l. An electric initiator of high-temperature stability which comprises atube open at both ends, a thick-walledrigid cylinder inch to about /2inch in length with an outer-to-inner diameter ratio of at least about2.0 and having a central bore containing from'0.03 to 0.6 grain of leadazide at a distribution of from 2.5 to 60 grains per foot and positionedaxially in said tube, and an electrical ignition assembly sealed withinone "end of said tube in igniting relationship to said lead azide, saidinitiator being of low brisance and resulting in substantially nooffensive noise upon initiation.

2. An initiator according to claim 1, wherein said ignition assemblycomprises a pair of lead wires connected. at their inner ends by abridgewire. I

3 An initiator according to claim 2, wherein said bridgewire issurrounded by a mass ofan ignition composition.

t 4. An initiator according to claim. 1, wherein said ignition assemblycomprises a pair of lead wires, thev inner ends of which are in contactwith a loose mass of an ignition composition.

5. An electric initiator as in claim 1 in combination with a length ofdetonatable explosive cord in said tube adjacent said rigid cylinder atthe end remote from the electrical ignition assembly.

References Cited in the file of this patent UNITED STATES PATENTS GreatBritain July 18, '1956

